Shock hazard protection system

ABSTRACT

The present invention teaches a new and novel system for protecting people and property against electrical shock. The invention includes a number of preferred and other embodiments which have this as their goal, but which represent a number of distinctive and novel approaches to solving prior art problems. By way of example only and without limiting the scope of this invention, these approaches include novel immersion detecting circuits, broken wire test circuits, electromechanical circuit breaking means including coil/plunger arrangements, and relay circuit breaking mechanisms cooperative with associated circuitry, all of which are able to be incorporated as a system wholly within the load (appliance) and its associated cord set (including a &#34;plug&#34;).

This is a continuation of application Ser. No. 618,271, filed Sep. 6,1990 and now abandoned.

Ser. No. 618271 is a continuation of application Ser. No. 471,258 filedJan. 26, 1990 and now abandoned.

Ser. No. 471,258 is a continuation of application Ser. No. 352,077,filed May 15, 1989 and now abandoned. Ser. No. 352,077 is a continuationof application Ser. No. 185,571, filed Apr. 25, 1988 and now abandoned.Ser. No. 185,571 is a continuation of application Ser. No. 082,259,filed Aug. 6, 1987 and now abandoned. Ser. No. 082,259 is a continuationof application Ser. No. 001,715, filed Jan. 9, 1987, and issued as U.S.Pat. No. 4,709,293 on Nov. 24, 1987. Ser. No. 001,715 is a continuationof application Ser. No. 880,396, filed Jun. 30, 1986 and now abandoned.Ser. No. 880,396 is a continuation of application Ser. No. 558,260,filed Dec. 5, 1983 and now abandoned.

This invention relates generally to electrical hazard prevention, andmore specifically to a shock hazard prevention system for disconnectingan electrical load from an electrical source when a shock hazardcondition exists within the load.

Devices for protecting human life and property against electrical shockand damage resulting from a shock hazard condition within an electricalload are known. For example, the model No. 6199 ground fault circuitinterruptor (GFCI) marketed by the assignee of the present invention iscapable of sensing and responding to the inadvertent grounding of theneutral conductor of an A-C electrical distribution system. It is noted,however, that in certain applications the utilization of such a GFCI isnot practical.

In particular, the GFCI is a relatively expensive and complex devicewhich requires the utilization of several transformers. In addition, theGFCI is often hardwired in a wall outlet or receptacle and is neitherportable nor readily disconnected. Thus, unless each outlet in which anelectrical device such as, for example, an appliance is to be utilizedis protected by a GFCI, the user of the appliance is subject to possibleinjury if a shock hazard condition should exist in conjunction with anon-protected outlet.

In addition, in certain environments the utilization of a conventionalGFCI would not afford any shock hazard protection to the user of anappliance. More specifically, a conventional GFCI device of the typeknown to applicants will not be effective or work if the user of anelectrical appliance drops the appliance in a plastic insulated bathtub.

Another potential drawback exists regarding the use of a GFCI forcertain types of portable electrical appliances such as, for example, ahair dryer. Although the owner of a hair dryer may have his or herresidence outlets adequately protected by GFCI devices, it is possiblethat other places, such as hotels, the residences of relatives, friends,etc., where it is desired to use the hair dryer may not be protected bysuch devices.

Accordingly, it is clear that what is needed is a shock hazard protectorwhich is associated with the appliance to be protected itself ratherthan with the electrical outlet in which the appliance is plugged andenergized. It is believed that prior to the present invention, this needhas gone unfulfilled.

A need exists for a shock hazard protector which possesses attributesincluding having a minimum number of components, reliability, cost andportability.

It is accordingly a general object of this invention to overcome theaforementioned limitations and drawbacks associated with the knowndevices and to fulfill the needs mentioned by providing a hazardprotection system having all of the desirable attributes noted above.

It is a particular object of the present invention to provide a shockhazard protector capable of disconnecting an electrical source from anelectrical load in response to the detection of a shock hazard conditionwithin the electrical load.

Another object of the present invention is to provide a shock hazardprotector capable of detecting and responding to a water-related shockhazard condition within an electrical appliance.

A further object of the present invention is to provide a shock hazardprotection system, as above, incorporating immersion detectioncircuitry.

A still further object of this invention is to provide a shock hazardprotection system, as above, wherein a feature is provided for detectinga possible break or discontinuity in a sensing or guard wire.

Yet another object of this invention is to provide a system, as above,wherein a solenoid-type electromechanical mechanism acts as a circuitbreaking or interrupting means.

A further object is to provide such a system wherein a relay andassociated circuitry and mechanical means enable the desired result.

Yet a further object of this invention is to provide a detection systemwhich detects or senses the presence of a conductive medium, and whichcauses an event in response thereto.

Another object of this invention is to provide a detection system whichdetects or senses the absence of the presence of a conductive medium,and which causes an event in response thereto.

Other objects will be apparent from the following detailed descriptionand practice of the invention.

The foregoing and other objects and advantages which will be apparent inthe following detailed description of the preferred embodiment, or inthe practice of the invention, are achieved by the invention disclosedherein, which generally may be characterized as a hazard protector. Thehazard protector includes detecting means associated with a load fordetecting a hazard condition within the load, an interrupting meansassociated with a source to which the load is operatively connected, andconducting means connected between the detecting means and theinterrupting means. In response to the detection of a hazard conditionwithin the load by the detecting means, the interrupting meansoperatively disconnects the source from the load.

Serving to illustrate exemplary embodiments of the invention are thedrawings, of which:

FIG. 1 is a perspective-type view of a hair dryer and its associatedcord set incorporating the system according to the present invention;

FIG. 2 is a block diagram of the shock hazard protector, in accordancewith the present invention;

FIG. 3 is a schematic diagram of one embodiment of the shock hazardprotector, in accordance with the present invention;

FIG. 4 is a schematic diagram of a second embodiment of the shock hazardprotector, in accordance with the present invention;

FIG. 5 is an enlarged partial sectional elevational view taken through acord set plug of a relay embodiment of the present invention;

FIG. 6 is a partial fragmentary sectional plan view taken along the line6--6 of FIG. 5;

FIG. 7 is a schematic circuit diagram of the embodiment of the presentinvention associated with FIGS. 5 and 6;

FIG. 8 is an elevational view of the cord set plug illustrated in FIG. 1and taken along line 8--8 of that same FIG. 1 depicting the assembledplug with its cover removed;

FIG. 9 is a partial sectional elevational view taken along line 9--9 ofFIG. 8;

FIG. 10 is a sectional view taken along line 10--10 of FIG. 8;

FIG. 11 is a fragmentary sectional view taken along line 11--11 of FIG.8; and

FIG. 12 is an exploded-type perspective view of components of thepresent invention illustrated in FIG. 8.

Referring now in more detail to the drawings, FIG. 1 is presented in itsform to illustrate a hair dryer 12 and its associated cord set 14 aswholly containing and constituting or comprising the shock hazardprotection system 10 of the present invention. It is applicants'intention and desire to emphasize here the fact that this inventioncontemplates an electrical appliance, such as of the personal healthcare type (hair dryers, etc.) which possesses all of the features andadvantages of the invention. It is also an intention of applicants toprovide the system of the present invention in the form of an OEMproduct available for sale to manufacturers of such appliances.

A plug assembly 16 is illustrated in FIG. 1 as including polarizedblades 18 extending from housing 20. Whereas commercially available hairdryers, as an example of a personal health care appliance, normallyinclude a cord set having two conductors or wires, a third wire 22 isillustrated in the case of cord set 14 electrically communicating with abare copper wire 24 whose path (in the example given in FIG. 1) includesproximity to and looped circuit near a dryer housing opening throughwhich an on-off switch assembly 26 extends, and thence upward to anotherloop proximate a dryer housing air inlet opening through which fan 28driven by motor 30 pulls air to be heated by heating coil 32 beforeexiting the dryer housing air outlet opening in which grill 34 ispositioned. After leaving the second loop described as being adjacentthe air inlet opening, wire 22 extends to a third loop adjacent grill34.

Since heater coil 32 carries and operates on current in the "hot" orphase line, and with the provision of conductor or wire 24 wired as partof the neutral side of the line, the presence of a conductive mediumsuch as, but not limited to, moisture or water between them will createa conductive path contemplated by the invention as enabling interruptionof current to the load 12. This embodiment is distinguishable fromanother embodiment of the present invention wherein a pair ofconductors, as opposed to a single guard or sensing conductor 24, arelocated at or near moisture/water housing penetration points.Configurations of one or more sensing or guard conductors other thanthose illustrated herein are contemplated as coming within the scope ofthis invention.

Referring to FIG. 2, a block diagram of a shock hazard protectoraccording to the present invention is illustrated. As shown therein, itcomprises a source operatively connected to a load by first and secondconductors 110 and 120, respectively, a detector 200 associated with theload, a control circuit 300 connected to the detector by a sensing orthird conductor 130, and an interruptor circuit 400 associated with thesource and connected to the control circuit 300. In the case of anelectrical A-C source, conductors 110 and 120 are tied to a phase andthe neutral terminal, respectively, of the A-C source.

In the normal mode of operation, that is, in the absence of a hazardcondition within the load, the control circuit 300, which changes from afirst state to a second state in response to the detection of a hazardcondition within the load, remains in the first state. Upon thedetection by detector 200 of a predefined fault or hazard conditionwithin the load, the control circuit 300 changes from the first to thesecond state, which causes the interruptor circuit 400 to operativelydisconnect the source from the load.

It is noted that the present invention contemplates certain applicationswhere the system sensitivity need not be accurately controlled, and thecontrol circuit 300 can be eliminated. In this situation the interruptorcircuit 400 is connected to the detector 200 by the third conductor 130,and responds directly to the detection by detector 200 of a hazardcondition within the load.

In either situation, the sensing or third conductor 130 communicates thepresence of the hazard condition within the load to the control circuit300 or the interruptor circuit 400.

Referring now to FIG. 3, a schematic diagram of one embodiment of theinvention particularly suited for use in conjunction with water-relatedshock hazard conditions within an electrical appliance operativelyconnected to an A-C source (not shown) by electrical conductors 110,120, respectively, is illustrated. As shown therein, detector 200comprises a pair of hazard or immersion detection conductors 210 and220, which are positioned in a non-contacting relationship and containedwithin the electrical load. A pair of immersion detection conductors 210and 220 are preferably located in proximity to each port of theappliance to be protected where water can enter.

For ease of description, it will be assumed that the appliance to beprotected only contains one port or opening through which water mayenter. For this situation, one end of one of the pair of immersiondetection conductors 210 is operatively connected to the phase terminalof an A-C source (not shown) via electrical conductor 110, and one endof the second of the pair of immersion detection conductors 220 isconnected to the load end of the third electrical conductor 130. Theother ends of immersion detection conductors 210, 220 are unconnectedand are maintained in a spaced-apart relationship, typically forexample, not more than one inch.

Shock hazard or immersion detection conductors 210, 220 may comprise,for example, a pair of bare electrical conductors or a pair ofconducting plates lines on a printed circuit board or other physicalconfigurations that will enable a conductive path between theunconnected ends thereof.

Control circuit 300 comprises a solid state switching control circuitand includes a first resistor R1 connected in-line between the gate of asilicon controlled rectifier SCR and the source end of the thirdelectrical conductor 130. Resistor R1 limits the current applied to thegate of the SCR. In addition, control circuit 300 includes a parallelnetwork comprising resistor R2, capacitor C and diode D connectedbetween the gate and cathode of the SCR. These components provide ameasure of noise immunity and protection against damage across the gateto cathode junction of the SCR.

Interruptor circuit 400 comprises an electromechanical interruptingcircuit and includes an energizing coil L and a first and second contactor switch S1, S2 connected in-line with the first and second electricalconductors 110, 120, respectively. Switches S1 and S2 are responsive tothe flow of current through energizing coil L and are closed when suchcurrent is not flowing. In response to the flow of such current theyswitch from the normally closed position to the shock hazard conditionopen position. One end of energizing coil L is connected to the firstelectrical conductor 110 and the other end thereof is connected to theanode of the SCR. The cathode of the SCR is operatively connected to thesecond electrical conductor 120.

The existence of a water-related shock hazard condition within theelectrical appliance is detected when both unconnected ends of the pairof immersion detection conductors 210, 220 are immersed in the water.More specifically, the immersion of both unconnected ends of the pair ofimmersion detection conductors 210, 220 causes the electrical A-C sourceto be operatively connected to the gate of the SCR via the path providedby the first electrical conductor 110, the first immersion detectionconductor 210, the electrically conducting path provided by the water inwhich the unconnected ends of the first and second immersion detectionconductors 210, 220 are immersed, the second immersion detectionconductor 220, the third electrical conductor 130, and resistor R1. Inresponse thereto, the SCR switches from the normally non-conductingstate to the shock hazard condition conducting state, thereby providinga path for current to flow through the energizing coil L causingswitches S1 and S2 to switch from the normally closed position to theshock hazard condition open position and thus operatively disconnectingthe A-C source from the electrical appliance.

To insure that the shock hazard protector is operable prior toutilization of the appliance it protects, a test circuit (not shown)comprising, for example, a resistor in series with a normally openswitch connected between the pair of immersion detection conductors 210,220 may be utilized. Closing the normally open switch causes theresistor to be connected across the immersion detection conductors and,if the shock hazard protector is operating, as described above, causesthe A-C source to be operatively disconnected from the appliance.Preferably, the test circuit is contained within the electricalappliance. In conjunction with said test circuit, diode D could bereplaced with a light-emitting-diode (LED). If the LED is illuminatedwith the test switch in the closed position it indicates that the shockhazard protector is not operating properly.

Preferably, electrical conductors 110, 120 and 130 comprise a three wireconductor having an A-C source compatible plug at the source end, thecontrol circuit 300 and interruptor circuit 400 are contained in theplug, and the detector 200 is contained within the appliance.

Thus in the case where the electrical appliance 15, is, for example, ahair dryer, the detector 200 would be located internally within thedryer and, as noted above, in proximity to each port thereof where watercan enter the dryer. It should be emphasized here that while water isgiven as the electrically conductive medium, this invention contemplatesa response to any electrically conducting medium, such that theappliance is electrically disconnected from the A-C source in responseto the presence of such a conductive medium.

Exemplary values for the circuit illustrated in FIG. 3 are as follows:R₁ -2000 ohms, R₂ -1000 ohms, C-0.1 microfarads, D-1N4004, SCR-2N5064.

Referring now to FIG. 4, a schematic diagram of a second embodiment ofthe present invention particularly suited for use in conjunction withwater-related shock hazard conditions within an electrical appliance isillustrated. This embodiment provides an additional feature not presentin the first embodiment illustrated in FIG. 3. In particular, theembodiment illustrated in FIG. 3, provides shock hazard protection ifany of electrical conductors 110, 120, individually or in combination,are broken, but does not provide shock hazard protection if electricalconductor 130 is broken. The embodiment illustrated in FIG. 4 providesan additional measure of shock hazard protection by rendering theelectrical appliance inoperative if any of electrical conductors 110,120 and 130, individually or in combination, are broken.

This additional measure of protection is provided by the addition of afirst diode D₁ connected in series between the second immersiondetection conductor 220 and the third electrical conductor 130, thereplacement of the capacitor connected between the gate and cathode ofthe SCR with an appropriate charging capacitor, the addition of a firstcharging circuit comprising resistor R_(N) and diode D_(N) connectedbetween the first and third electrical conductors 110, 130, the additionof a zener diode in series with the diode connected between the gate andcathode of the SCR, the addition of a second charging circuit comprisingresistor Rp and diode Dp connected between the first electricalconductor 110 and the gate of the SCR, and the elimination of resistorR₂ connected between the gate and cathode of the SCR.

The operation of the circuit illustrated in FIG. 4 is as follows.Assuming that the sensing or third conductor 130, is intact, theappliance is not immersed in water and that it is energized, during thenegative half cycle of the A-C signal on electrical conductor 110 anegative charging path via diode D_(N), resistor R_(N), third conductor130, resistor R₁ provides charge to capacitor C, thereby charging itnegatively. During the positive half cycle diode D_(N) blocks, however,a positive charging path via resistor Rp and diode Dp provides charge tocapacitor C, thereby charging it positively. Since the time constant ofresistor R_(p) and capacitor C, is roughly 33 times greater than thetime constant of resistor R_(N) and capacitor C, the capacitor C chargesmuch faster in the negative sense, so that under steady state conditionsa negative voltage exists on the gate of the SCR thereby keeping it in anon-conducting state. In order to limit that negative voltage to a valuethat would not damage the gate to cathode junction of the SCR a threevolt zener diode is added in series with diode D₂, also in parallel withcapacitor C.

The next condition to look at is a broken third conductor 130. Underthis condition a negative charging path no longer exists for thenegative voltage to be impressed on capacitor C, and, therefore duringpositive half cycles capacitor C will discharge positively andeventually the voltage on the gate of the SCR will get high enough totrip the SCR, causing it to switch to the conducting state therebyoperatively disconnecting the A-C source from the appliance, putting youin a safe condition. Exemplary values for the circuit illustrated inFIG. 4 are as follows: D₁, D₂, D_(N), D_(p) -1N 4004, R_(N) -30,000ohms, R_(p) -1,000,000 ohms, R₁ -2000 ohms, C-1 microfarad, SCR-2N5064,Z-3 volt zener diode.

Preferably, the components comprising the first charging circuit R_(N),D_(N) and diode D₁ are contained within the electrical appliance and arewaterproof, and the components comprising the second charging circuitRp, Dp and the zener diode D are contained in the plug.

It is noted that with minor modifications the above described inventionhas many other applications. For example, in the situation where theelectrical appliance comprises a power tool, such as a drill having anelectrically conducting housing, the teachings of the present inventionmay be utilized by eliminating immersion detection conductor 220 andconnecting the third electrical conductor 130 to the electricallyconducting housing. The immersion in water of the unconnected end ofshock hazard detection conductor 210 provides an electrically conductivepath between the shock hazard detection conductor and the electricallyconducting housing of the drill causing, as described above, the drillto be operatively disconnected from the A-C source.

Referring now to an embodiment of the present invention which utilizesthe approach of a relay mechanism to accomplish the circuit interruptinggoal of the invention, FIG. 5 illustrates a shock hazard protectorembodiment of a plug assembly 510 formed with a housing with base andcover body halves 512 and 514, respectively, joined at a housingreference line 516. A strain relief 518 comprises part of cord 520 and,in cooperative combination with the shape and contour of annularsurfaces 522, 524, 526 and 528, serves as a means for protecting theintegrity of electrical connections during use.

Blades 530 extend outwardly from surface 532 of housing half 512 andserve the function of matingly and electrically engaging electricalcontacts within a receptacle (not shown) or electrical outlet in thehome, for example. A fixed contact 534 is associated and integral witheach of the blades 530, contacts 534 being fixed or stationary asopposed to movable when assembled.

A pair of movable contacts 536 are provided and are integral with leafsprings 538 which, in turn, are anchored by means of eyelets 540extending through openings in an end portion of the leaf springs 538spaced from the movable contacts 536. These eyelets further extendthrough openings through a printed circuit board 542 supported by ledges544 and 546 adjacent upstanding walls 548 and 550, as shown in FIG. 5.

A tab 552 associated with each leaf spring 538 further anchors the leafsprings to the printed circuit board in spaced relationship with respectto the aforesaid eyelets, thereby serving an additional function ofpreventing undesirable rotation of the leaf springs 538, assuringalignment and reliably repeated engagement between the fixed and movablecontacts 534 and 536, respectively. Leaf springs 538 are configured tonormally bias the movable contacts 536 away from the fixed contacts 534when in an unstressed condition, thereby normally interrupting anelectrical path between these contacts. The ends of leaf springs 538 areformed with upstanding flanges 554 to which conductors 556 areconnected.

A plunger or core 558 is disposed vertically within a bobbin coil 560,as illustrated in FIG. 5. A reset button 564 contacts the uppermostportions of plunger 558, while a butterfly cross bar 562 extendslaterally across the plug housing and in contact with upper surfaces ofleaf springs 538. The upward biasing forces of leaf springs 538 maintainthe cross bar 562, plunger 558 and reset button 564 in the positionsshown in FIG. 5, while a metal strap 566 extends about portions of coil560 as shown. The cross sectional shape of reset button 564 ispolygonal, such as square, to prevent rotation thereof, while the crosssectional shape of core or plunger 558 is round to provide maximumelectromagnetic efficiency in its interaction with bobbin coil 560. FIG.6 illustrates in a cross sectional view what applicants refer to as the"butterfly" with arms 568 being splayed outwardly from a center rivetmember 570 aligned with plunger 558.

In operation, power for the printed circuit board electronic componentsis supplied by a copper path on the board via pins 572 extendingdownwardly from the bobbin coil 560. Prior to a shock hazardpredetermined condition, the system of FIG. 5 is "set" by means ofdepressing set or reset button 564 inwardly, which results in movementof the plunger and the cross bar against the opposing biasing forces ofleaf springs 538. This depression of the set or reset button will resultin movement of the leaf springs until the movable contacts engage thefixed contacts, thereby completing an electrical circuit.

The completion of the electrical circuit just described results incurrent flow to the bobbin coil which, in turn, electromagnetically"keeps" and holds the plunger in its depressed position until aninterruption of such current flow. The interengagement of the movableand fixed contacts further serves to enable the supply of power to theload or appliance with which the inventive assembly of FIG. 5 isassociated, again, until an interruption in current flow to the bobbincoil.

In the event of the presence of a shock hazard condition, as a result ofthe operation of circuitry of FIG. 7 described in detail below, currentto the bobbin coil is interrupted, with the result that the upwardbiasing forces of leaf springs 538 rapidly cause a separation of themovable contacts away from the fixed contacts, thereby in turn causingan interruption of power from the source through the blades to the loador appliance.

Referring now to FIG. 7 of the drawings, the aforesaid circuitryassociated with the device of FIG. 5 is illustrated with like componentsin FIGS. 5 and 7 carrying like reference characters. With the relay ofFIG. 5 being fed with half wave rectified alternating current, orpulsating direct current, there is some current flow during the negativehalf cycle or the half cycle other than that when line current isflowing. A free wheeling diode FWD continues current flow.

The main contacts M_(C) are normally open. When it is desired to turn onthe appliance after plugging it into a receptacle power source set orreset button 564 is depressed, bringing movable contacts 536 intoengagement with fixed contacts 534. This applies half wave rectifieddirect current to the bobbin coil. This results in applying a voltagefrom the phase line through the double pole single throw switch DPST,through a diode D₁, thence through the bobbin coil, with the other endof the coil going through another contact of the double pole switch toneutral. Thus, by pushing the switch or reset button, the coil isenergized, and the main contact M_(C) is closed.

Once the main contact M_(C) is closed, a parallel path for the currentis provided through another diode D₂, such that there is current flowfrom phase through diode D₂ through the coil with its free wheelingdiode in parallel with it, thence through the collector of a transistorQ₁, the emitter of the transistor Q₁ being connected to neutral. Thetransistor is kept on by a resistor going from phase to the base. R₁ isthe resistor between phase and the base.

Once the coil energizes itself as described, the transistor is turned onand then the momentary contact in the DPST is released and the coil isself-holding. Should the load or appliance be dropped into water,creating a shock hazard condition, the current in a sense line isrectified by diode D₃ and a resistor R₂ puts a negative voltage onto thebase of the transistor. A capacitor C₁ is provided between thetransistor base and the emitter which will essentially store whatevervoltage was present to smooth it out. By setting the value of R₂relatively small with respect to the value of R₁, the time constant ofthe negative current is shorter than that of the positive current and inthis way there is a negative charge turning off the transistor with theresult that the movable contacts separate from the fixed contacts (FIG.5).

The reader is cautioned not to construe the examples presented in thisspecification, such as in describing hair dryers or other appliances, aslimiting the invention to these examples. Any electrical appliance orapparatus with which a shock hazard may be associated is contemplated asbeing favorably affected by the advantages and features of the presentinvention.

Referring now to another embodiment of the present invention illustratedin FIGS. 8-12, a novel electromechanical and electromagnetic combinationserves a circuit interrupting or breaking function, as well as otherfunctions. In FIG. 8 a plug assembly 600 of the type designated withreference character 16 in FIG. 1 is shown with cover housing half 602removed to illustrate base housing half 604 with its assembledsubassemblies in place. A pair of movable contact arms 606 and 608 areeach anchored at their respective angled depending legs 610 and 612within slots or recesses 614 and 616 of base housing half 604. Near ends618 and 620 of movable arms 606 and 608, respectively, remote from theirends 610 and 612, silver contacts 622 and 624 are respectively rivetedto arms 606 and 608.

Flexible conductors 626 are welded at 628 to depending legs 610 and 612at one of their ends, and at their other ends 630 the flexibleconductors are welded to plug insertion blades 632. Blades 632 areconfigured with mounting shoulders 634 so as to be held relativelyintegral with base 604 when assembled.

Movable contact arms 606 and 608 are normally biased in the directionshown in phantom lines within FIG. 11 such that they bias the silvercontacts 622 and 624 away from fixed silver contacts 636 and 638 whichare riveted to fixed contact terminals 640 and 642, respectively. Thefixed contact terminals 640 and 642 themselves are physically andelectrically connected to a printed circuit board 644 which carries oneof the electrical circuit embodiments described above and contemplatedby the invention.

A latch member 646 formed with a tang 648 is associated with eachmovable contact arm and each is mounted and pivoted at its upper end onpivot points 650 formed on legs 652 of a set/reset button 654. At theirlower ends 656, latches 646 are formed with a downward bend or leg, asviewed in FIG. 11, these latter legs giving the latches structuralstability for added reliability. The full lines of FIG. 11 illustratelatches 646 in their latched or set position, with tangs 648 holding theends of movable contact arms 606 and 608 such that movable silvercontacts 622 and 624 are in physical and electrical engagement withfixed silver contacts 636 and 638, thereby enabling current flow throughblades 632 from a source such as an electrical receptacle to a load,such as hair dryer 12.

Reset button 654 is normally biased in a direction away from blades 632by means of helical compression springs 658 shown in FIGS. 9 and 12, forexample. Springs 658 are held captive between and exert forces againstopposing surfaces 660 and 662 of the underside of the reset button 654and a metallic frame 664 (see FIG. 9). Set/reset button 654 is visibleto the user through a window 668 formed within cover housing half 602and preferably carries indicia of the type illustrated in FIG. 8 to drawattention to its function.

When the movable contact arms 606 and 608 are in the positions shown inFIG. 11 in phantom outline, resting against a wall 666 formed in basehousing half 604, such that the electrical circuit is in an interruptedstate with the movable and fixed contacts spaced in opposition withrespect to one another, the user of the present invention is able toclose the circuit, assuming no hazard condition is present, bydepressing with his or her finger the set/reset button 654. Thisdepression of the button 654 causes latches 646 to move in the samedirection as the movable button 654 and in sliding engagement with theends of the movable contact arms 606 and 608 until and such that tangs648 ride over these arm ends. Release of the formerly depressed button654 results in its only partially returning under the influence ofsprings 658 towards its original position, with a resulting pulling ofthe movable contacts 622 and 624 into engagement with their respectiveopposing contacts 636 and 638 by latch tangs 648 against the undersidesof the movable arm ends, thereby setting the system and closing thecircuit. Latches 646 and their tangs 648 hold the movable contacts inthe last position just described until a hazard condition is sensed ordetected. In such an event, a plunger 670 shown in FIGS. 8 and 9 asbeing normally biased away from its associated winding or coil 672 bymeans of a helical compression spring 674 is caused to rapidly approachthe core of coil 672 as a result of its being energized. Plunger 670 isformed with a neck 676 adjacent its end remote from coil 672, with whicha clevis 678 of what will here by referred to as a banger 680 matinglyengages. Banger 680 is further formed with pairs of trip and reset dogs682 and 684 movable paths that coincide with latch 646. Uponenergization of coil 672, trip dogs 682 rapidly come into contact withand "bang" against the surfaces of latches 646 facing wall 666, forciblydisengaging the latches 646 and their tangs 648 from the movable contactarms, with the result that these arms return to their rest positionsagainst wall 666, and interrupt current flow through the movable andfixed contacts. Once the current is interrupted, the compression forceswithin spring 674 cause the plunger 670 and its interconnected banger680 to return to the position illustrated in FIG. 9, with the reset dogs684 coming into contact with and biasing the latches 646 against theends of the movable contact arms 606 and 608.

Frame 664 comprises part of the magnetic circuit associated with anoperating winding or coil 672, and for that purpose encloses a portionof the coil. A strain relief 686 formed in the insulation of a cord set688 is shown in FIGS. 8 and 9 held between opposing annular walls 690and 692, respectively, of housing halves 602 and 604 which, in turn, arereleasably secured together by means of fasteners 694. Cord set 688corresponds to the cord set 14 illustrated in FIG. 1.

FIG. 8 illustrates the printed circuit board 644 in broken-line outlinein the position it occupies atop the banger assembly and the fixedcontacts. FIG. 8 further illustrates the three wires, phase/neutral 696and the guard or sensing wire 698 which extend through and as part ofcord set 688, through the strain relief 686, and into the confines ofplug assembly 600. Sensing wire 698 corresponds to the third wire 22 ofFIG. 1 which electrically communicates with a sensing wire in the load,such as sensing wire 24 of FIG. 1, and wire 698 is coupled to the PCboard 644 while the phase and neutral lines are electrically secured tothe fixed contact terminals 640 and 642. Terminals 640 and 642 are softsoldered to the PC board 644 by means of mounting tabs 700.

The present invention thus provides the user with a shock hazardprotection system which: has a reponse time that conforms toUnderwriters Laboratories requirements; is trip free; possesses a doublepole interrupting mechanism with an air gap switch; operates withreverse polarity; requires only a 2 pole receptacle; operates in anungrounded environment, such as a plastic tub; is of a reasonable sizeand cost; provides the user with a visible trip indication; meetsUnderwriters Laboratories overload, short circuit, and endurancerequirements; possesses electrical noise immunity so as to minimizefalse tripping; provides protection in the event the cord is broken,with proper polarity assumed; provides adequate strain relief; is usablewith a combination switch/receptacle; and provides protection whetherthe load or appliance switches are on or off, or are at medium or highsettings.

The embodiments of the present invention herein described and disclosedare presented merely as examples of the invention. Other embodiments,forms and structures coming within the scope of this invention willreadily suggest themselves to those skilled in the art, and shall bedeemed to come within the scope of the appended claims.

What is claimed is:
 1. In combination with an electrical loadoperatively connected to an A-C source by a cord set including a firstand second electrical conductor each having a source end and a load end,respectively, and a plug compatible with said A-C source, a shock hazardpreventing circuit comprising:a third electrical conductor having asource end and a load end; a first and second shock hazard detectionconductor each having a connected end and an unconnected end,respectively, positioned in a non-contacting relationship and containedwithin said load, the connected end of said first shock hazard detectionconductor being connected to the load end of said first electricalconductor, the connected end of said second shock hazard detectionconductor being connected to the load end of said third electricalconductor, and the unconnected ends of said first and second shockhazard detection conductors being maintained in a spaced-apartrelationship; an interrupting circuit contained within said plug andincluding an energizing coil and a first and second switch responsive tothe flow of current through said energizing coil, said first switchbeing operable between a normally closed position and a shock hazardcondition open position and connected in-line with said first electricalconductor, said second switch being operable between a normally closedposition and a shock hazard condition open position and connectedin-line with said second electrical conductor; a switching controlcircuit contained within said plug and including a silicon controlledrectifier operable between a normally non-conducting state and a shockhazard condition conducting state, a first resistor connected in seriesbetween the gate of said silicon controlled rectifier and the source endof said third electrical conductor, and network means comprising aplurality of electrical elements connected in parallel with each other,said network means being connected between the gate and the cathode ofsaid silicon controlled rectifier for providing noise immunity anddamage protection to said silicon controlled rectifier; such that theimmersion in an electrically conductive medium of the unconnected endsof said first and second shock hazard detection conductors provides anelectrically conductive path between said first and second shock hazarddetection conductors causing said A-C source to be operatively connectedto the gate of said silicon controlled rectifier resulting in theswitching of said silicon controlled rectifier from the normallynon-conducting state to the shock hazard condition conducting statethereby providing a path for current flow through said energizing coiland causing said first and second switches to switch from the normallyclosed position to the shock hazard condition open position and thusoperatively disconnecting said A-C source from said electrical load, andwherein said network means comprises a network comprising a secondresistor, a capacitor in parallel with said second resistor, and a diodeconnected in parallel with said capacitor.
 2. The combination recited inclaim 1 wherein the cathode of said diode is connected to said gate ofsaid silicon controlled rectifier.
 3. In combination with an electricalload contained within an electrically conducting housing and operativelyconnected to an A-C source by a cord set including a first and secondelectrical conductor each having a source end and a load end,respectively, and a plug compatible with said A-C source, a shock hazardpreventing circuit comprising:a third electrical conductor having asource end and a load end; a shock hazard detection conductor containedwithin said electrical load and maintained in a non-contactingrelationship with said electrically conducting housing, one end of saidshock hazard detection conductor being connected to the load end of saidfirst electrical conductor and the other end of said shock hazarddetection conductor being unconnected and maintained in a spaced-apartrelationship with said electrically conducting housing, and saidelectrically conducting housing being connected to the load end of saidthird electrical conductor; an interrupting circuit contained withinsaid plug and including an energizing coil and a first and second switchresponsive to the flow of current through said energizing coil, saidfirst switch being operable between a normally closed position and ashock hazard condition open position and connected in-line with saidfirst electrical conductor, and said second switch being operablebetween a normally closed position and a shock hazard condition openposition and connected in-line with said second electrical conductor; aswitching control circuit contained within said plug and including asilicon controlled rectifier operable between a normally non-conductingstate and a shock hazard condition conducting state, a first resistorconnected in series between the gate of said silicon controlledrectifier and the source end of said third electrical conductor, andnetwork means comprising a plurality of electrical elements connected inparallel with each other, said network means being connected between thegate and the cathode of said silicon controlled rectifier for providingnoise immunity and damage protection to said silicon controlledrectifier; such that the immersion in an electrically conductive mediumof the unconnected ends of said first and second shock hazard detectionconductors provides an electrically conductive path between said firstand second shock hazard detection conductors causing said A-C source tobe operatively connected to the gate of said silicon controlledrectifier resulting in the switching of said silicon controlledrectifier from the normally non-conducting state to the shock hazardcondition conducting state thereby providing a path for current flowthrough said energizing coil and causing said first and second switchesto switch from the normally closed position to the shock hazardcondition open position and thus operatively disconnecting said A-Csource from said electrical load and wherein said network meanscomprises a network comprising a second resistor, a capacitor connectedin parallel with said second resistor, and a diode connected in parallelwith said capacitor.
 4. The combination recited in claim 3 wherein thecathode of said diode is connected to said gate of said siliconcontrolled rectifier.
 5. In combination with an electrical applianceoperatively connected to an A-C source by a cord set including a firstand second electrical conductor each having a source end and anappliance end, respectively, and a plug compatible with said A-C source,a shock hazard preventing circuit comprising:a third electricalconductor having a source end and an appliance end and contained withinsaid cord set; a first and second shock hazard detection conductor eachhaving a connected end and an unconnected end, respectively, positionedin a non-contacting relationship and contained within said electricalappliance, the connected end of said first shock hazard detectionconductor being connected to the appliance end of said first electricalconductor, the connected end of said second shock hazard detectionconductor being connected to the appliance end of said third electricalconductor, and the unconnected ends of said first and second shockhazard detection conductors being maintained in a spaced-apartrelationship; an interrupting circuit contained within said plug andincluding an energizing coil and a first and second switch responsive tothe flow of current through said energizing coil, said first switchbeing operable between a normally closed position and a shock hazardcondition open position and connected in-line with said first electricalconductor, and said second switch being operable between a normallyclosed position and a shock hazard condition open position and connectedin-line with said second electrical conductor; a switching controlcircuit contained within said plug and including a silicon controlledrectifier operable between a normally non-conducting state and a shockhazard condition conducting state, a first resistor connected in seriesbetween the gate of said silicon controlled rectifier and the source endof said third electrical conductor, and network means comprising aplurality of electrical elements connected in parallel with each other,said network means being connected between the gate and the cathode ofsaid silicon controlled rectifier for providing noise immunity anddamage protection to said silicon controlled rectifier; such that theimmersion in an electrically conductive medium of the unconnected endsof said first and second shock hazard detection conductors provides anelectrically conductive path between said first and second shock hazarddetection conductors causing said A-C source to be operatively connectedto the gate of said silicon controlled rectifier from the normallynon-conducting state to the shock hazard condition conducting statethereby providing a path for current flow through said energizing coiland causing said first and second switches to switch from the normallyclosed position to the shock hazard condition open position and thusoperatively disconnecting said A-C source from said electrical load andwherein said network means comprises a network comprising a secondresistor, a capacitor connected in parallel with said second resistor,and a diode connected in parallel with said capacitor.
 6. Thecombination recited in claim 5 further the cathode of said diode isconnected to said gate of said silicon controlled rectifier.